1. Field of the Invention
This invention relates to heat developable photographic silver halide materials and process for developing and stabilizing an image with these materials. In one of its aspects it relates to a heat developable photographic element comprising a support having thereon a certain combination of materials including an image-forming combination comprising (i) a certain silver imidazoline-2-thione, with (ii) an organic, silver halide developing agent and a binder. In another aspect it relates to a heat developable photographic composition comprising the described imaging combination. A further aspect of the invention relates to a process of developing and stabilizing an image in a heat developable photographic element containing the described imaging combination.
2. Description of the State of the Art
It is known to obtain an image in a photographic material by what is described as dry processing with heat. Such photographic materials are sometimes described as heat developable photographic materials or photothermographic materials. Such heat developable photographic materials or photothermographic materials, after imagewise exposure, are heated to provide a developed image in the absence of separate processing solutions or baths. In some cases, the developed image is also stabilized, such as with an incorporated stabilizer or stabilizer precursor in the photographic material. Typical heat developable imaging materials or photothermographic materials are described, for example, in U.S. Pat. No. 3,152,904 of Sorensen et al, issued Oct. 13, 1964; U.S. Pat. No. 3,457,075 of Morgan et al, issued July 22, 1969; U.S. Pat. No. 3,152,903 of Shepard et al, issued Oct. 13, 1964; U.S. Pat. No. 3,392,020 of Yutzy et al, issued July 9, 1968; British Specification No. 1,161,777 published Aug. 20, 1969; and U.S. Pat. No. 3,801,321 of Evans et al, issued Apr. 2, 1974.
The most commonly employed silver salts in such heat developable photographic materials are silver salts of long-chain fatty acids such as silver behenate and silver stearate. It has been desirable to replace these silver salts of long-chain fatty acids to enable use of aqueous or hydrophilic compositions which further enable the use of conventional silver halide technology, especially silver halide gelatino emulsion technology in heat developable photographic materials. Use of silver behenate as a source of silver in the described heat developable materials is not particularly compatible with aqueous formulations of silver halide photographic materials. Other silver salts or complexes have been proposed for the described heat developable photographic materials. These include, for example, silver salts of benzotriazole, silver salts of saccharin and related silver salts or complexes. These other silver salts are described, for example, in heat developable photographic materials in U.S. Pat. No. 3,617,289 of Ohkubo et al, issued Oct. 2, 1971; U.S. Pat. No. 3,666,477 of Goffe, issued May 30, 1972; U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972; U.S. Pat. No. 3,832,186 of Masuda et al, issued Aug. 27, 1974; British Specification No. 1,205,500 published Sept. 16, 1970; U.S. Pat. No. 3,689,270 of Anderson et al, issued Sept. 5, 1972; U.S. Pat. No. 3,785,830 of Sullivan et al, issued Jan. 15, 1974; and copending U.S. application Ser. No. 684,699 of deMauriac, filed May 10, 1976, now abandoned. While many of these silver complexes or salts can provide an image in a heat developable photographic silver halide material, they often provide undesirable processing temperature latitude, undesired photographic speed, undesired image tone, do not provide a stable image after processing, or a combination of one or more of these problems.
It has also been desirable to provide heat developable and stabilizable photographic materials which enable use of commonly employed silver halide developing agents in the photographic material. Heat developable photographic materials often have used reducing agents not commonly employed in silver halide photography which require costly processes of preparation. It has been desirable to eliminate this problem with a heat developable and stabilizable photographic material which better enables use of conventional developing agents, such as phenolic developing agents and ascorbic acid developing agents, which do not adversely affect the post-processing stabilization of the material. Typical reducing agents which have been used in heat developable photographic materials are described, for example, in U.S. Pat. No. 3,672,904 of deMauriac, issued June 27, 1972 and other of the described patents. Commercially available photothermographic materials have used such reducing agents as 2,2'-methylenebis(4-methyl-6-tertiarybutylphenol) which is not a conventional silver halide developing agent.
Photographic materials which are not heat developable photographic materials are known containing nitrogen acids. Nitrogen acids, for example, are described in photographic materials in Belgian Pat. No. 790,955 issued May 3, 1973 and U.S. Pat. No. 3,933,507 of Von Konig et al, issued Jan. 20, 1976. Silver salts of certain nitrogen acids have also been found useful in photographic materials which are heat processable as described in copending U.S. application Ser. No. 684,699 of deMauriac, filed May 10, 1976, now abandoned. None of these references, however, indicate or suggest answers to the described problems in heat developable photographic materials which are required to be stable after processing without a subsequent processing step or separate incorporated stabilizer or stabilizer precursor.
Silver salts of a variety of organic compounds are known for various purposes in photographic materials. For example, some of the silver salts of organic compounds can be useful as incorporated couplers such as described in U.S. Pat. No. 2,353,754 of Peterson, issued July 18, 1944 and U.S. Pat. No. 3,794,496 of Manhart, issued Feb. 26, 1974. Silver salts of certain heterocyclic thione compounds have also been found useful in heat developable materials such as described in U.S. Pat. No. 3,785,830 of Sullivan et al, issued Jan. 15, 1974. These references, however, do not describe a heat developable and stabilizable photographic material containing a silver 1-methyl, 1-ethyl or 1-phenyl-4-imidazoline-2-thione in an image-forming combination as described herein.
Imidazoline-2-thione compounds have been used in heat developable photographic materials for post-processing stabilization purposes. These materials are described, for example, in U.S. Pat. No. 3,839,041 of Hiller, issued Oct. 1, 1974 and U.S. Pat. No. 3,801,330 of Brinckman et al, issued Apr. 2, 1974. Neither of these patents indicate that the described imidazoline-2-thione compounds can provide a silver salt or complex as described herein which provides both a source of silver in an image-forming combination and provides post-processing stabilization without the need for a separate image stabilizer or stabilizer precursor.
There has been a continuing need for improved heat developable photographic materials containing image-forming combinations comprising a silver salt imidazoline-2-thione with an organic silver halide developing agent. As illustrated in the comparative examples in the following description, selection of a suitable silver imidazoline-2-thione can in many cases provide a heat developable material which does not have the desired post-processing stability or lacks other desired properties in combination with a desired developed image. This need has been particularly important for heat developable photographic materials which have the desired degree of photosensitivity provided by photographic silver halide and which enable the use of conventional gelatino silver halide emulsion technology.